Sample concentration apparatus

ABSTRACT

Apparatus for concentration of a sample, to be delivered to a remote analysis mechanism, including a vertically mounted, quartz-lined heater, a water cooled condenser which is tefloncoated to eliminate cross-contamination and which has a sandwichlike construction to facilitate disassembly and cleaning, and an extended corrugated teflon tube for transporting the sample to the remote analysis mechanism.

United States Patent [54] SAMPLE CONCENTRATION APPARATUS 14 Claims, 5 Drawing Figs.

[52] U.S. Cl 159/4, 202/188, 711/613, 73/421, 159/30 s 1] Int. Cl B01d l/l6, B01d l/30, G0ln1l/00, 801d 3/00 [50] Field ofSearch 159/1, 16,

30, DIG. 2, 16 A, DIG. 1, 44, 4, 4 B, DIG. 15,28; 202/234,188;203/40,49, 100; 73/61.3, 421; 55/67, 197, 386; 165/166, 167, 73, 111

[56] References Cited UNITED STATES PATENTS 2,793,939 5/1957 I-Ialtmeier.... 23/261 2,873,799 2/1959 Earley et a1 159/6W 3,104,947 9/1963 Switzer et al. 159/16A 3,276,510 10/1966 Austin et 31.... 159/16A 3,480,513 11/1969 Martin 159/16AX 799,621 9/1905 Brewtnall 165/166 861,485 7/1907 Stokes 202/188 991,905 5/1911 Sleeper... 202/188X 2,676,000 4/1954 Ekwall 165/167 2,937,856 5/1960 Thomson 165/167X 3,174,326 3/1965 Carle et al.. 73/23.1 3,357,157 12/1967 ODonnell 55/67X 3,374,607 3/1968 Fisher et a1. 55/197X 3,518,059 6/1970 Levy 55/67X Primary Examiner- Norman Yudkoff Assistant Examiner-J. Sofer Attorney-Willis M. Ertman ABSTRACT: Apparatus for concentration of a sample, to be delivered to a remote analysis mechanism, including a vertically mounted, quartz-lined heater, a water cooled condenser which is teflon-coated to eliminate cross-contamination and which has a sandwichlike construction to facilitate disassembly and cleaning, and an extended corrugated teflon tube for transporting the sample to the remote analysis mechanism.

PATENTED JUN 1 5 197:

SHEEI 1 BF 2 PATENTEU JUN] 519m SHEET 2 BF 2 ASPIRATING GAS v EVAPORATOR 2 x O a COOLANT ANT 7 P 8% M0 7 wO mw /mw m 3 SAMPLE CONCENTRATEON APPARATUS SUMMARY OF THE INVENTION This invention relates to concentration of a sample to be delivered to an analysis mechanism (e.g., a flame, are or spark discharge, radio frequency excited plasma, or other thermal process) for excitation or dissociation.

Prior art apparatus for delivery of such a sample to such a mechanism has either not provided for concentration at all or has included concentration means which were bulky, were difficult to disassembly and clean between sample changes, had ineffective heater means, were of limited applicability (e.g., could be used only with an atomic absorption instrument), and presented the danger of a flashback.

It is a primary object of the invention to provide apparatus for concentration which substantially eliminates the foregoing problems in an efficient and inexpensive concentrator configuration.

The invention features apparatus, for the treatment of a sample solution to be delivered to an analysis mechanism, comprising an aspirator for aspirationof the sample solution with a transport gas, a evaporator in which the transport gas and aspirated sample are heated, a condenser in which the vapor of the heated sample solution is condensed and the residue dried to provide a particulate sample, and delivery means for transport of the dried particulate sample to an analysis mechanism; wherein, the surfaces of the condenser and the delivery means open to contact with the transport gas and sample in each of the means have a nonporous, chemically inert coating whereby cross-contamination between various samples is substantially eliminated. In preferred embodiments the invention also features the mounting of the heater means of the evaporator vertically so as to avoid the collection of a pool of sample in the aspiration means end of the heater means; an arrangement in which the transport gas and sample solution are subjected to a scrubbing action along the hot wall of the heater means during which the transport gas and sample solution are heated by conduction; the provision of a quartz liner component installed in said heater means, thereby to facilitate cleaning of the apparatus; and a water cooled condenser structure constructed in a sandwichlike configuration to facilitate disassembly for cleaning.

Other objects, features, and advantages will appear from the following description of a preferred embodiment of the invention, taken together with the attached drawings thereof. This description of a preferred embodiment is in an illustrative and not a limiting sense as other embodiments of the invention will be apparent to those skilled in the art. In the drawings:

FIG. I is a perspective view of a concentrator constructed according to the invention:

FIG. 2 is a partially exploded and partially broken away view of the concentrator of HG. 1;

FIG. 3 is a transverse sectional view of the concentrator of FIG. 1 taken in part along a baffle element 90;

FIG. 4 is a section taken at 4-4 of FIG. l; and

FIG. 5 is a section taken at 5-5 of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT For purposes of illustration, the following description and the drawings deal specifically with a concentrator associated with a burner head for use in an atomic absorption instrument. It will be apparent, however, that the concentrator described is constructed so as to be compatible with other excitation or dissociation mechanisms as mentioned in the first paragraph of this specification.

The general arrangement of the preferred embodiment illustrated in the drawings is best described by reference to FIGS. 1 and 2, where reference numeral it) refers generally to the concentrator. The major components of the concentrator consist of a frame member 12, an aspirator-evaporator unit 14 mounted vertically above frame member 12, a condenser l6 mounted beneath and adjacent the inclined plate 18 of frame member 12, and an extended flexible tube 20 which connects the condenser 16 with a burner head 22. In an atomic absorption instrument the burner head 22 produces a flame F. An optical axis A extends between a light source LS and a photocell PC, and the radiation passing along the optical axis from the light source to the photocell is modified by the flame as a function of material in the flame. I

As can best be seen in FIG. 2, the concentrator is designe for easy removal of the major components to facilitate cleaning. The aspirator-evaporator unit 14- is attached to condenser 16 by a plurality of screws 24 (best seen in H0. 4). Condenser 16- is supported by support bars 26 which are of L-shaped cross section and which are in turn supported by bolts 30. The bolts 30 suspend through holes 32 in plate 18 of frame member 12 and have threaded lower ends 27 which screw into threaded holes 34 in support bars 26. Tube 20 fits over one end of a coupling element 36 which in turn passes through port 38 in plate 18 of frame member 12. The other end of coupling element 36 is threaded and screws into threaded port 40 in condenser 16.

The details of construction of the aspirator and the evaporator can best be illustrated by reference to FIG. 4. The aspirator comprises a chamber 42, within which the sample delivery tube 44 terminates; and a tube 46 communicating with chamber 42 which delivers the pressurized support gas to the chamber 42. The aspirator is mounted on the evaporator by means of an easily removable clamp 48.

In the preferred heater construction 15 feet of 22 Nichrome V wire, indicated by numeral 50, is wound on 3 inches of a 4 as inches long XI inches o.d. mullite tube 52, potted with ceramic inside a second one-eighth inch wall thickness mullite tube 54. Insulation 56 is /2 inch wrinkled aluminum foil. A shield or cover 58 is provided to protect the operator from burns. The heater is lined with a 6 inches long X1 541 inches o.d. quartz tube 60. The quartz tube 60 should be of minimum wall thickness available consistent with necessary strength. A thickness of 1 to l k millimeters has been found to be adequate. Resilient seal 62 seals the quartz tube to heater base member 64. The wire 50 is connected to a power source (not shown) which is preferrably variable.

The details of condenser construction are best shown in FIGS. 2 and 3. The condenser 16 is constructed in a fourlayer, sandwichlike configuration and is about 16 it inches long and about 6 inches wide. The uppermost layer 70 comprises plate 18 of frame member 12 and longitudinal barrier walls 74 and 74a and ribs 75 and 75a protruding vertically downward therefrom, thereby forming three separate chan nels 76, 78, beneath plate 18.

The next layer, 82, comprises a single solid plate (except for apertures noted below) with a smooth, chemically inert, coating 84 of a fluorocarbon polymer on its lower surface. A nonporous polytetrafluoroethylene has been found to be an adequate material for coating $4. The use of such a material for coating 84, as well as further uses mentioned below, yields a concentrator which is easily cleaned and in which cross-contamination between samples can be eliminated.

The third layer, 86, comprises a continuous peripheral portion 88, a multiplicity of hollow angularly disposed baffle elements extending inwardly therefrom, and a floor member 92 located about seven eights inch below the upper surface of peripheral portion 88 and filling the interstitial spaces between baffle elements 90 and peripheral portion 88. The bafi'le elements 90 are arranged in two sets extending inwardly from opposite sides of peripheral portion 80, the elements in each set being parallel to one another and all intersecting the peripheral portion 88 obliquely such that, when the condenser 16 is in place in the assembled preconcentrator, the baffle elements all point in the downstream" direction. As best seen in FIG. 2, the baffle elements 90 are so placed, and are of such length and angle to peripheral portion. 88, that each baffle element extends beyond the midpoint of the space between the longitudinal sides of peripheral portion 88. The preferred condenser configuration provides a width between longitudinal peripheral portions 88 of 3 inches and baffle elements 90 which are 3 inches long and which are inclined at an angle of 10 to a normal from peripheral portion 5%. This configuration assures that the heated support gas and sample solution will have no unobstructed path through the condenser 16.

As best illustrated in FIG. 3, the upper surface of floor member 92, the baffle elements 90 and peripheral portion 88 have a coating 94 of nonporous polytetrafluoroethylene. This coating, and that on the lower surface of second layer 82, provide, when the condenser is assembled, a smooth chemically inert channel 95 through the condenser 16 for the heated support gas and sample solution.

The fourth layer comprises a plate member 96 which, when the condenser is assembled, fits flush against the downwardfacing surface of peripheral portion 38 of third layer 86. As best seen in FIG. 3, the peripheral portion 88 extends somewhat below the downward-facing surface 93 of floor member 92 thereby creating a channel 98, beneath depressed plate member 92 and above the fourth layer plate member 96, forcooling water, as described in detail below.

As best seen in FlGS. 2 and 3, an O-ring MN) is disposed in a peripheral groove in portion 88 and provides a seal between second layer 82 and third layer 86, thereby sealing channel 95.

The cooling water enters the condenser structure through inlet pipe 1102 which is sealed in any conventional fashion in orifice 1104 (see FIG. 3). Orifice we, in turn, communicates directly with channel 76 of uppermost layer 70. After passing the length of channel 76, the water enters a vertical passage 1106 (see H6. 2) which extends through second layer 82 and portion 88 and communicates with the void (channel 98) between the third layer member $6 and fourth layer member 96. The cooling water then flows up the inclined condenser 16 through channel 98 and then, via a connecting passage 107 through portion 88 and plate 82, to channel 78 in uppermost layer 70. The water flows down channel 78 and then around the end of rib 75 and cylindrical wall MW between channels 78 and 80, as shown in FIG. 2. Finally, the water flows through channel 80 and leaves the condenser via outlet tube 108.

The condenser 16 also includes a water release stopcock M2 which permits the drainage of water from the condenser for disassembly of the condenser, and condensate drain tube 114 which communicates with channel 95 and which terminates in a remote condensate sump (not shown) to permit condensate drainage without disassembly of the condenser.

The Communication of the heater-aspirator unit l4 and of the coupling element 36 with channel 95 of the condenser is illustrated in FIG. 4 and 5, respectively.

Resilient seals 101, M3, and W5 are provided to seal channel 95 and the water channels.

Extended flexible tube 26 is constructed of a corrugated, nonporous chemically inert polytetrafluoroethylene. It has been found that, when used with a burner head as the excita tion mechanism, an extended tube of approximately two feet in length yields a quieter flame than one of substantially shorter length.

The preconcentrator is prepared for operation by closing water release stopcock 2, connecting the source of cooling water (e.g., tap water) to inlet pipe 102, and connecting the heater unit to its power supply (not shown).

The sample solution is then aspirated through nozzle 34 by the transport gas. The mixture is heated through scrubbing contact with the walls of quartz liner 6b as it passes through the heater unit and thence to channel 95 of condenser 16. The solvent portion of the sample solution is condensed out of the sample solution-transport gas mixture in the cooled condenser channel 95. The particulate sample and transport gas then proceed up through coupling member 36 wherein they are mixed with the flame supporting medium (i.e., C H which enters through tube 116. This ultimate mixture is then delivered, via extended flexible tube 20, to the burner head 22.

Disassembly of the condenser, when desired, is accomplished as follows: First water release stopcock 112 is opened.

Condenser disassembly may then proceed with bolts 30 being partially unscrewed from threaded holes 34 in support bars 26. This releases the compressive force on the layers of the condenser 16, thereby permitting third and fourth layers 86 and 9b to slide longitudinally with respect to frame member 12 and to first and second layers and 82. Removal of third and fourth layers 86 and 96 permits maximum ease and efficiency of cleaning of the complexly shaped baffle elements 90 and channel of the condensers third layer 86. It also exposes for easy cleaning the flat lower surface of second layer 82 which forms the top of channel 95.

For further disassembly of the concentrator, extended flexible tube 29 is disconnected from coupling member 36 thereby permitting the latter to be unscrewed from condenser 16 and removed entirely from the concentrator assembly. Heateraspirator unit M is removed by merely removing mounting screws 24 which pass through base member 64 and screw into threaded holes in plate member 72 of first layer 70 of condenser 16. Thus the entire concentrator unit provides ease of maintenance and change of components as desired.

Other embodiments will occur to those skilled in the art and are within the following claims.

What we claim is:

11. Apparatus for the treatment of a sample solution prior to delivery to an analysis mechanism for analysis of the sample comprising a condenser having an inlet, an outlet, structure defining a channel through which a sample in gaseous suspension flows, and means to cool said condenser channel defining structure to subject the sample to condensing action and provide a dried particulate sample, said condenser channel defining structure including a plurality of components in a sandwichlike assembly, at least one of the components of said sandwichlike assembly being releasably mounted in said assembly to facilitate disassembly for cleaning, so that, upon release and removal of said releasably mounted component, all surfaces within said condenser which during sample treatment are in contact with said sample are exposed,

a heater-evaporator mounted on said condenser and having an outlet connected to the inlet of said condenser, an inlet, and structure defining a channel between said evaporator inlet and said evaporator outlet through which a mixture of sample and transport gas passes, and means for heating said heater channel defining structure to vaporize solvent in said sample solution,

an aspirator having a sample inlet, a transport gas inlet, and an outlet through which the mixture of the sample and transport gas passes, said aspirator being mounted on top of said heater and having its outlet connected to said heater inlet,

and delivery means connected to the outlet of said condenser for transport of said dried particulate sample to said analysis mechanism, the surfaces of said condenser and said delivery means which during sample treatment are in contact with said transport gas and sample having a nonporous, chemically inert coating.

2. The apparatus as claimed in claim 1 wherein said heater channel defining structure defines a vertical passage between said aspirator and said condenser.

3. The apparatus as claimed in claim 1 wherein said heater channel defining structure includes a heated wall surface and said transport gas and sample solution are heated by conduction in a scrubbing action during passage along the hot wall of said heater channel defining structure.

4. The apparatus as claimed in claim 3 wherein said heated wall surface is defined by a removable quartz cylinder.

5. The apparatus of claim 17 wherein said sandwichlike assembly comprises four layers.

6. The apparatus of claim 5 wherein the bottom two of said four layers are releasably mounted.

7. The apparatus of claim 1 wherein said condenser channel defining structure has a longitudinal axis and two peripheral longitudinal parallel walls, and further including baffles that protrude into said channel alternately from said two longitudinal parallel walls of said channel, each said baffle extending beyond said longitudinal axis of said chamber.

8. The apparatus of claim 7 wherein said baffles protrude from said two longitudinal parallel walls at an angle of approximately to a line normal to said parallel walls.

9. Apparatus for the treatment of a sample solution prior to delivery to an analysis mechanism, for analysis of the sample, comprising an aspirator having a sample inlet for aspiration of the sample solution with a transport gas, a transport gas inlet, and an outlet through which a mixture of the sample and transport gas passes,

an evaporator having an inlet connected to the outlet of said aspirator, an outlet, and structure defining a channel between said evaporator inlet and said evaporator outlet through which the mixture of said sample and said transport gas passes, and means for heating said channel defining structure to vaporize solvent in said sample solution, said aspirator being mounted on top of said evaporator,

a condenser having an inlet connected to said evaporator outlet, and outlet, structure defining a channel through which the heated mixture of sample and transport gas flows, and means to cool said condenser channel defining structure to condense the sample solvent and provide a dried particulate sample residue, said evaporator being mounted on said condenser, said condenser channel defining structure including a plurality of components in a sandwichlike configuration assembly, at least one of the components of said sandwichlike assembly being releasably mounted in said assembly to facilitate disassembly for cleaning, so that, upon release and removal of said releasably mounted component, all surfaces within said condenser which during sample treatment are in contact with said sample solution and transport gas are exposed,

and delivery means connected to the outlet of said condenser for transport of said dried particulate sample residue to said analysis mechanism.

10. The apparatus of claim 9 wherein said condenser channel defining structure has a longitudinal axis and two peripheral longitudinal parallel walls, and further includes baffies that protrude into said channel alternately from said two longitudinal parallel walls of said channel, each said baffle extending beyond said longitudinal axis of said chamber.

11. The apparatus of claim 9 wherein said baffles protrude from said two longitudinal parallel walls at an angle of approximately 10 to a line normal to said parallel walls.

12. The apparatus of claim 9 wherein said sandwichlike assembly comprises four layers.

13. The apparatus of claim 12. wherein the bottom two of said four layers are releasably mounted.

14. Apparatus for the concentration of a sample solution to be delivered to an analysis mechanism, said apparatus comprising a frame member having an inclined upper face, an aspirator for aspiration of the sample solution with a transport gas, an evaporator in which said transport gas and aspirated sample solution are heated and the solvent evaporated, a condenser in which said the vapor of heated sample solution is condensed and the residue dried to provide a particulate sample, and delivery means for transport of said dried particulate sample to said analysis mechanism;

said aspirator being mounted on said evaporator, said evaporator being mounted above and upon said upper face of said frame member and comprising an electric heater unit that includes a coil of resistance wire disposed between two electrically insulating tubes and a quartz liner inside said heater unit that defines a vertically oriented heater channel through which a mixture of said sample solution and said transport gas flows from said aspirator to said condenser;

said condenser being mounted beneath and substantially parallel to said upper face of said frame member and comprising a fourayer, sandwichltke assembly wherein the first and second layers of said assembly cooperate to define an upper cooling water chamber, the second and third layers of said assembly cooperate to define a channel for passage of the heated transport gas and sample through the condenser, and the third and fourth layers of said assembly cooperate to define a lower cooling water chamber, said channel defined by said second and third layers being lined with a nonporous, chemically inert polytetrafluoroethylene coating, a resilient seal between said second and third layers for sealing said channel, said condenser first and second layers being mutually compressed by means of bolts and longitudinally extending compression bars, said bolts passing through said frame member and being threaded into mating holes in said bars, said bars being disposed to under lap the lowermost layer of said condenser; and

said delivery means comprising corrugated, nonporous chemically inert polytetrafluoroethylene tubing extending between said analysis mechanism and a coupling element connected between said tubing and said channel defined by said cooperating second and third layer of said condenser. 

1. Apparatus for the treatment of a sample solution prior to delivery to an analysis mechanism for analysis of the sample comprising a condenser having an inlet, an outlet, structure defining a channel through which a sample in gaseous suspension flows, and means to cool said condenser channel defining structure to subject the sample to condensing action and provide a dried particulate sample, said condenser channel defining structure including a plurality of components in a sandwichlike assembly, at least one of the components of said sandwichlike assembly being releasably mounted in said assembly to facilitate disassembly for cleaning, so that, Upon release and removal of said releasably mounted component, all surfaces within said condenser which during sample treatment are in contact with said sample are exposed, a heater-evaporator mounted on said condenser and having an outlet connected to the inlet of said condenser, an inlet, and structure defining a channel between said evaporator inlet and said evaporator outlet through which a mixture of sample and transport gas passes, and means for heating said heater channel defining structure to vaporize solvent in said sample solution, an aspirator having a sample inlet, a transport gas inlet, and an outlet through which the mixture of the sample and transport gas passes, said aspirator being mounted on top of said heater and having its outlet connected to said heater inlet, and delivery means connected to the outlet of said condenser for transport of said dried particulate sample to said analysis mechanism, the surfaces of said condenser and said delivery means which during sample treatment are in contact with said transport gas and sample having a nonporous, chemically inert coating.
 2. The apparatus as claimed in claim 1 wherein said heater channel defining structure defines a vertical passage between said aspirator and said condenser.
 3. The apparatus as claimed in claim 1 wherein said heater channel defining structure includes a heated wall surface and said transport gas and sample solution are heated by conduction in a scrubbing action during passage along the hot wall of said heater channel defining structure.
 4. The apparatus as claimed in claim 3 wherein said heated wall surface is defined by a removable quartz cylinder.
 5. The apparatus of claim 17 wherein said sandwichlike assembly comprises four layers.
 6. The apparatus of claim 5 wherein the bottom two of said four layers are releasably mounted.
 7. The apparatus of claim 1 wherein said condenser channel defining structure has a longitudinal axis and two peripheral longitudinal parallel walls, and further including baffles that protrude into said channel alternately from said two longitudinal parallel walls of said channel, each said baffle extending beyond said longitudinal axis of said chamber.
 8. The apparatus of claim 7 wherein said baffles protrude from said two longitudinal parallel walls at an angle of approximately 10* to a line normal to said parallel walls.
 9. Apparatus for the treatment of a sample solution prior to delivery to an analysis mechanism, for analysis of the sample, comprising an aspirator having a sample inlet for aspiration of the sample solution with a transport gas, a transport gas inlet, and an outlet through which a mixture of the sample and transport gas passes, an evaporator having an inlet connected to the outlet of said aspirator, an outlet, and structure defining a channel between said evaporator inlet and said evaporator outlet through which the mixture of said sample and said transport gas passes, and means for heating said channel defining structure to vaporize solvent in said sample solution, said aspirator being mounted on top of said evaporator, a condenser having an inlet connected to said evaporator outlet, and outlet, structure defining a channel through which the heated mixture of sample and transport gas flows, and means to cool said condenser channel defining structure to condense the sample solvent and provide a dried particulate sample residue, said evaporator being mounted on said condenser, said condenser channel defining structure including a plurality of components in a sandwichlike configuration assembly, at least one of the components of said sandwichlike assembly being releasably mounted in said assembly to facilitate disassembly for cleaning, so that, upon release and removal of said releasably mounted component, all surfaces within said condenser which during sample treatment are in contact with said sample solution and transport gas are exposed, and delivery means connected to the outlet of saId condenser for transport of said dried particulate sample residue to said analysis mechanism.
 10. The apparatus of claim 9 wherein said condenser channel defining structure has a longitudinal axis and two peripheral longitudinal parallel walls, and further includes baffles that protrude into said channel alternately from said two longitudinal parallel walls of said channel, each said baffle extending beyond said longitudinal axis of said chamber.
 11. The apparatus of claim 9 wherein said baffles protrude from said two longitudinal parallel walls at an angle of approximately 10* to a line normal to said parallel walls.
 12. The apparatus of claim 9 wherein said sandwichlike assembly comprises four layers.
 13. The apparatus of claim 12 wherein the bottom two of said four layers are releasably mounted.
 14. Apparatus for the concentration of a sample solution to be delivered to an analysis mechanism, said apparatus comprising a frame member having an inclined upper face, an aspirator for aspiration of the sample solution with a transport gas, an evaporator in which said transport gas and aspirated sample solution are heated and the solvent evaporated, a condenser in which said the vapor of heated sample solution is condensed and the residue dried to provide a particulate sample, and delivery means for transport of said dried particulate sample to said analysis mechanism; said aspirator being mounted on said evaporator, said evaporator being mounted above and upon said upper face of said frame member and comprising an electric heater unit that includes a coil of resistance wire disposed between two electrically insulating tubes and a quartz liner inside said heater unit that defines a vertically oriented heater channel through which a mixture of said sample solution and said transport gas flows from said aspirator to said condenser; said condenser being mounted beneath and substantially parallel to said upper face of said frame member and comprising a four-layer, sandwichlike assembly wherein the first and second layers of said assembly cooperate to define an upper cooling water chamber, the second and third layers of said assembly cooperate to define a channel for passage of the heated transport gas and sample through the condenser, and the third and fourth layers of said assembly cooperate to define a lower cooling water chamber, said channel defined by said second and third layers being lined with a nonporous, chemically inert polytetrafluoroethylene coating, a resilient seal between said second and third layers for sealing said channel, said condenser first and second layers being mutually compressed by means of bolts and longitudinally extending compression bars, said bolts passing through said frame member and being threaded into mating holes in said bars, said bars being disposed to under lap the lowermost layer of said condenser; and said delivery means comprising corrugated, nonporous chemically inert polytetrafluoroethylene tubing extending between said analysis mechanism and a coupling element connected between said tubing and said channel defined by said cooperating second and third layer of said condenser. 